"The tunnel, dark as the grave, cold, damp and silent. How beautiful look heaven and earth again when you emerge from such gloom!" That's how Walt Whitman once described America's oldest subway tunnel. The 1844 construction and subsequent operation of this half-mile tunnel under Brooklyn's Atlantic Avenue were plagued by bloodshed: A workman shot his foreman at point-blank range, another laborer was buried alive under a collapsed wall, and a train beheaded a passenger who fell onto the tracks. After being sealed up in 1861, legend has it the dank passageways sheltered river pirates, smugglers, and, later, bootleggers distilling whiskey pumped to a speakeasy above. Nineteen-year-old Bob Diamond rediscovered the tunnel in 1981 by crawling 70 feet underground through a dirt-choked section less than two feet high. Diamond joined forces with the city to excavate the entrance and open the tunnel to the public. Now, each month he leads brave groups down a ladder under a manhole cover in the middle of a busy Brooklyn street. Below ground, they creep through the shadowy tunnel, shining flashlights on the debris of its cursed past.